Abstract

Local field potentials (LFPs) reflect the averaged dendrosomatic activity of synaptic signals of large neuronal populations. In this study, we investigate the selectivity of LFPs and single neuron activity to semantic categories of visual stimuli in the medial temporal lobe of nine neurosurgical patients implanted with intracranial depth electrodes for clinical reasons. Strong selectivity to the category of presented images was found for the amplitude of LFPs in 8% of implanted microelectrodes and for the firing rates of single and multiunits in 14% of microelectrodes. There was little overlap between the LFP- and spike-selective microelectrodes. Separate analysis of the power and phase of LFPs revealed that the mean phase was category-selective around the θ frequency range and that the power of the LFPs was category-selective for high frequencies around the γ rhythm. Of the 36 microelectrodes with amplitude-selective LFPs, 30 were found in the hippocampus. Finally, it was possible to readout information about the category of stimuli presented to the patients with both spikes and LFPs. Combining spiking and LFP activity enhanced the decoding accuracy in comparison with the accuracy obtained with each signal alone, especially for short time intervals.

c2007 Massachusetts Institute of Technology.
We thank all patients for their participation and Eric Behnke,
Tony Fields, Emily Ho, Eve Isham, and Charles Wilson for
technical assistance. We also would like to thank Gabriel
Kreiman and Daniel Rizzuto for helpful discussions. This work
was supported by grants from the NINDS, NIMH, NSF, DARPA,
EPSRC, the Office of Naval Research, the W.M. Keck Foundation
Fund for Discovery in Basic Medical Research, the Gordon
Moore Foundation, the Sloan Foundation, and the Swartz
Foundation for Computational Neuroscience.